Roadmap for the development of control strategies for liver fluke

What are we trying to achieve and why? What is the problem we are trying to solve?

Main problem is to achieve effective protection from a vaccine, consistent between individuals, and suitable for field use.
Scalability for commercial use requires either recombinant vaccines or a system for producing effective native antigen
vaccines at scale; both routes are challenging.
Deciding what level of protection is useful in the field depends on further questions:

• How long should a vaccine protect livestock and what levels of protection would be sufficient to prevent disease and production losses?
• What would be the best way of administering the vaccine to reduce production losses, in combination with other control approaches including chemoprophylaxis and grazing management?

What are the scientific and technological challenges (knowledge gaps needing to be addressed)?

• Why can protection be elicited using native antigen and not, so far, recombinant antigens?
• How do immune evasion and modulation strategies by the fluke circumvent vaccine efficacy?
• The levels of efficacy required will vary across livestock species and between regions, depending on climatic context and local farm management practices.
• Vaccine efficacy requirements may also be different in calves or lambs that co-graze with their dams.

What approaches could/should be taken to address the research question?

For logistical, financial and animal welfare reasons, it will be practically impossible to test all possible scenarios by vaccine trials in the field. Evaluating vaccine efficacy requirements through mathematical modelling is a valuable tool to help define useful levels of protection and to model integrated use of vaccines with other parasite control measures.
Ultimately, producing a vaccine effective enough to make an epidemiological impact is the main solution route.

What else needs to be done before we can solve this need?

At present, regulatory authorities are not familiar with registration of helminth vaccines. As it is unlikely that
any vaccine will obtain efficacy levels that are comparable with those of modern anthelmintics (or vaccines against viruses and bacteria), regulatory authorities will need to be informed about thresholds for duration and level of protection that are sufficient to reduce infection to a level that does not interfere with animal welfare and productivity.

Existing knowledge including successes and failures

One modelling study study has been published attempting to set epidemiologically useful thresholds for protection in the field, but this is theoretical only and acknowledged unexplored variation across climates and management systems.